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This page contains frequently asked questions related to units.

FAQ

In which units is the mass entered?

Per the

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CSI

Analysis Reference Manual (Joints and Degrees of Freedom > Masses, page 39), the mass values must be given in consistent mass units (W/g). Also please note that the program uses force, length and temperature as primary units, while the mass is secondary unit. Based on this the following reasoning is made:

(1) If the "Ton, m, C" set of units is chosen, the "ton" actually represents ton-force (tonf).

(2) The mass of 1 tonm (1000 kg) has a weight of 1 tonf (9810 N).

(3) However, the mass must be entered into the program in consistent units (W/g as mentioned above), therefore the mass corresponding to 1 tonf weight (remember that the weight is the primary unit) would be entered as W/g = 1 tonf / (9.81 m/s^2) = 0.102 tonf * s^2 /m.

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Related Incident:

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    The following explanation is provided in Incident 30267: In SAP2000, the basic units are Force (lb, kip, N, kN, etc.), Length (ft, in, m, mm, etc.), Time (second), and Temperature (F, C). Mass is a derived unit and SAP2000 does not use lb or kip for mass units, they are only used for force units. Weight has units of F, where F is force. CONSISTENT mass units are given by F/(L/T^2), where L is length, T is time, and the mass units are simply force divided by UNIT acceleration.
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